In the paints and coatings industry, traditional solvent-borne paints and coatings are being replaced with waterborne system due to concerns regarding the impact of Volatile Organic Compounds (VOC) to human health and the environment. In addition, recently enacted environmental legislation requires the reduction of the amount of Volatile Organic Compounds (VOC) in coatings. For example, SCAQMD (South Coast Air Quality Management District) in California and OTC (Ozone Transport Commission) in the East Coast states, have required reduced amounts of VOC emissions of coatings & paints products, especially architectural and industrial paints & coatings. (After application of a coating to a substrate, VOCs slowly evaporate into the surroundings.)
These regulations are forcing polymers and paints manufactures to develop lower VOC products. However, the waterborne technologies for lower or zero VOC paints & coatings have many challenges and drawbacks especially in achieving the key performances compared to solvent-based coatings or high VOC paint products.
For example, reduced or limited open time or wet edge time is one of the major challenges of low or zero VOC paints & coatings. Open time of the paints is defined as a period of time that the wet paint remains workable after it has been applied to a substrate and allow corrections such as rebrushing or rolling without resulting in any surface defects. Wet edge time refers to the time when a painter applies fresh paint to a wet painted area and the fresh paint can merge in without resulting in visible lap in the dried coating films.
Open time of waterborne or aqueous-based latex paints has been a major challenge compared to solvent-based paints because of fast evaporation of water in the aqueous-based paints. Typically, the open time of solvent-borne coatings and paints, which typically contain the organic solvents such as toluene or xylene, is about 30 to 45 minutes.
For the traditional waterborne coatings & paints, one traditional method is to add ethylene glycol or glycol ethers (or other high VOC solvents) to increase the open time or wet-edge time. It is believed that such organic solvents remain in or around the latex particles and assist the latex particle in moving freely even when all of the water has evaporated from the aqueous paint system. The use of glycols in aqueous coating formulations has various advantages to aqueous products, e.g., by increasing open time/wet edge time, providing freeze thaw stability, aiding polymer coalescence, and improving flow and leveling.
However, in low or no VOC formulations, the use of these glycols are substantially reduced or eliminated. When latex binders are formulated into low or near zero VOC aqueous coatings and paints, i.e., the use of glycols and other VOC's are substantially reduced or eliminated, the open time was reduced significantly and is in the range of 3-5 minutes. The insufficient open time resulted in poor application on larger substrates as well as surface defects in coating films.
Thus, it is desirable to have coatings and paint formulations without or with substantially reduced VOC content, which would include additives such as open-time additives, coalescing agents, freeze-thaw agents, etc. Latex binder manufactures are thus forced to develop low VOC binders to meet the requirements of paints and coatings industry, yet at the same time meeting or exceeding coating performance standards set in the industry.